1. Field of the Invention
The present invention relates to an injection molding machine, and more particularly, to a controller of the injection molding machine which controls a process position of an injection member in the injection molding machine at every predetermined cycle.
2. Description of the Related Art
An injection molding machine M, as illustrated in FIG. 1, includes a mold clamping section Mc and an injection section Mi on a machine base. The mold clamping section Mc opens and closes a mold 40 (movable-side mold 40a and stationary-side mold 40b). The injection section Mi heats and melts a resin material (pellet) and injects the molten resin into a cavity of the mold 40.
First, the mold clamping section Mc will be described. The mold clamping section Mc is made up of a movable platen 30, a rear platen 31, a toggle 32, a stationary platen 33, a cross head 34, a mold clamping servo motor M3 which is configured to move the movable platen 30 backward and forward, a servo motor M4 which is configured to push out an ejector pin for ejecting a molded article from the mold, and a ball screw shaft 38 which is driven by the mold clamping servo motor M3. The stationary platen 33 is fixed onto a machine base. The stationary platen 33 and the rear platen 31 are connected to each other by a plurality of tie bars 41. The movable platen 30 is disposed to move (backward and forward) along the tie bars 41 between the stationary platen 33 and the rear platen 31 by an operation of the toggle 32.
The movable-side mold 40a is attached to the movable platen 30, and the stationary-side mold 40b is attached to the stationary platen 33. The mold 40 is configured by the movable-side mold 40a and the stationary-side mold 40b. The ball screw shaft 38 is driven by the mold clamping servo motor M3, the cross head 34 attached to the ball screw shaft 38 moves backward and forward, and thus a position of the movable platen 30 can be changed. In this case, when the cross head 34 moves forward (moves to the right direction in FIG. 1), the movable platen 30 moves forward through the toggle 32 and thus the mold is closed. Then, a mold clamping force is generated by multiplying an impellent force due to the mold clamping servo motor M3 by toggle magnification, and the mold clamping is performed by the generated mold clamping force.
Next, the injection section Mi will be described. A nozzle 12 is attached to the leading end of an injection cylinder portion 10, and a screw 1 is inserted into a cylinder 5 of the injection cylinder portion 10. The screw 1 is rotated by a screw rotating servo motor M2 and moved in an axial direction of the screw 1 by a screw moving back and forth servo motor M1. Further, reference numeral 14 denotes a hopper which supplies resin to the cylinder 5. FIG. 1 illustrates a state where the injection nozzle 12 of the leading end of the injection cylinder portion 10 in the injection section Mi is closely contacted with a resin injection port of the stationary platen 33. In this state, a resin melted by the rotation of the screw 1 is injected into the mold 40 (movable-side mold 40a and stationary-side mold 40b) by a forward movement of the screw 1.
A molding operation using the injection molding machine M will be described. When the mold clamping servo motor M3 rotates in a normal direction, the ball screw shaft 38 rotates in the normal direction, and the cross head 34, which is engaged with the ball screw shaft 38 by the screw, moves forward (to the right direction in FIG. 1). Then, the toggle 32 is actuated and the movable platen 30 moves forward.
When the movable-side mold 40a attached to the movable platen 30 comes in contact with the stationary-side mold 40b attached to the stationary platen 33 (a state in which the mold is closed), a mold clamping process is started. In the mold clamping process, when the mold clamping servo motor M3 is further driven in the normal direction, the mold clamping force is generated in the mold 40. Then, when the screw moving back and forth servo motor M1 provided in the injection section Mi is driven and the screw 1 moves forward in the axial direction, the molten resin is filled in a cavity space which is formed in the mold 40 (movable-side mold 40a and stationary-side mold 40b).
When the mold opening process is performed, the mold clamping servo motor M3 is driven in a reverse direction to rotate the ball screw shaft 38 in the reverse direction. Accordingly, the cross head 34 moves backward, and the movable platen 30 moves (backward) in a direction approaching the rear platen 31. When the mold opening process is completed, the servo motor M4 is actuated to push out the ejector pin (not illustrated) for ejecting the molded article from the movable-side mold 40a. Thus, the ejector pin is pushed out from an inner surface of the movable-side mold 40a, and the molded article within the movable-side mold 40a is pushed out from the movable-side mold 40a. 
In the injection cylinder portion 10, the screw 1 is rotated by the screw rotating servo motor M2 to melt the resin, and thus the molten resin is fed forward. Then, the screw 1 moves backward by being rotated with this resin pressure by the screw moving back and forth servo motor M1 to perform a metering. Thereafter, the screw 1 moves forward by the screw moving back and forth servo motor M1 to inject the molten resin into the mold 40. In order to prevent a backflow of the resin during the injection, a check valve 3 is provided at the leading end of the screw 1.
The injection cylinder portion 10 in the injection molding machine M will be described with reference to FIG. 2.
The screw 1 is inserted into the cylinder 5, and a screw head 2, the check valve 3, and a check seat 4 are provided at the leading end of the screw 1. The check valve 3 is disposed to be movable in the axial direction of the screw 1 to a reduced diameter portion between body portions of the screw 1. The check seat 4 is formed in the reduced diameter portion of the leading end of the screw 1, provided on the side of the body of the screw, to come in close contact with the check valve 3 and to close a resin passage.
In a metering process, the screw 1 rotates, and the resin pellet supplied from the back side of screw 1 is melted by shearing heat generated by the rotation of the screw 1 and heat from a heater (not illustrated) provided at an outside of the cylinder 5 into which the screw 1 is inserted. The molten resin raises the resin pressure at a rear of the check valve 3 to generate a force for pushing the check valve 3 forward. When the check valve 3 is pushed forward, the resin of a rear screw compression portion 6 is fed to the front of the check valve 3 through a gap between the check valve 3 and the reduced diameter portion of the leading end of the screw to raise a pressure in the cylinder 5 ahead of the screw head 2.
When the resin pressure at the front of the check valve 3 exceeds a predetermined pressure, the screw 1 is pushed backward and thus the pressure at the front of the check valve 3 is reduced. Since the pressure at the rear of the check valve 3 is higher than the pressure at the front of the check valve 3 as the screw 1 further rotates, the continuously melted resin is fed to the front of the check valve 3. When the screw 1 moves backward to a predetermined range, the rotation of the screw is stopped and the metering process is completed.
Next, an injection process is started. When the screw 1 moves forward to fill the resin in the mold 40, the pressure of resin accumulated in the front of the screw head 2 rises. Thus, the check valve 3 moves backward and comes in close contact with the check seat 4 to close the resin passage to prevent the backflow of the molten resin in a backward direction of the screw 1.
The backflow of the resin occurs toward the back side from the front side of the check valve 3 until the resin passage is closed by the check valve 3 after the injection is started. The backflow occurs in the resin passage, but may also occur in a gap formed by a difference between an outer diameter of the check valve 3 and an inner diameter of the cylinder 5. When the injection molding machine is continuously used for a long time, the check valve 3 and the cylinder 5 are worn out and the amount of backflow is varied. Since the amount of backflow has an influence on the amount of resin filled in the mold, the quality of the molded article is influenced by the amount of backflow.
Further, in the compression portion 6 of the screw, the inside of the cylinder 5 is sometimes deposited with contaminants such as color additives or resin burning. The presence of the contaminants also has an influence on the quality of the molded article. In order to remove the contaminants from the inside of the cylinder 5, it is necessary to purge with a detergent or to disassemble and clean the injection cylinder portion 10, and thus costs and man-hours are required.
Japanese Patent Application Laid-Open No. 2008-302527 discloses the facts that when an injection molding machine is continuously used, a check valve and the inner wall of a cylinder are worn out, the backflow of resin occurring toward the back side from the front side of the check valve is increased, and the backflow of resin has an influence on the amount of resin filled in a mold and on the quality of a molded article. Further, the above-mentioned patent document discloses, as a measure of such influence, a technique which detects a screw rotation force due to backflow of resin occurring toward the back side from the front side of the check valve and estimates the worn state of the check valve by a change in physical quantities such as a magnitude of a peak value of the screw rotation force, a time point of peak appearance, a position of the screw at that time or the like.
According to the technique disclosed in the above-mentioned patent document, by detecting the screw rotation force due to the backflow of resin, it is possible to calculate a progression of the worn state of the check valve or the like up to the present date and predict a future progression of wear from the estimation result, but the above-mentioned patent document does not specifically disclose the way of reducing the wear amount.